Fuel tank vapor and emission control systems may be used to control the flow of fuel vapors from a vehicle's fuel tank and also to control the relative pressure of the fuel tank. Vapors may be vented to a canister or other similar vapor control structure where hydrocarbon vapors are stored and which is also connected to the engine air inlet.
Fuel tanks may generate fuel vapors during various operating phases and these vapors may be directed to a canister or other component responsible for storing them, and then purging them regularly to the admission header of the engine. Periodic purging of stored vapors may be necessary during operation of the vehicle. To conduct the purge, the fuel system is operated to control flow of vapor from the storage canister to the engine air inlet, and atmospheric air is admitted to purge the canister.